1. Technical Field
The pen invention relates to a scanning-type image display device.
2. Related Art
In recent years, a scanning-type image display device has been proposed that displays images by raster scanning a beam of light such as laser light on a projection surface.
Since this device can achieve a perfect black by stopping the supply of laser light, a higher contrast display is possible compared to a projector or the like that uses a liquid crystal light valve, for example.
Moreover, since an image display device that employs laser light is characterized by having a high color purity due to the laser light being a single wavelength and by readily shaping (focusing) the beam due to high coherence, it is expected to be used as a high-definition display that realizes high resolution and high color reproduction.
Also, in contrast to liquid crystal displays and plasma displays or the like, since the scanning-type image display device does not have fixed pixels, there is no concept of pixel number and so has the advantage of easily changing the resolution.
In order to generate an image with the scanning-type image display device, it is necessary to scan light in two dimensions using scanners such as a polygon mirror or a galvano-mirror.
Although there is a method of scanning light in two dimensions while moving a single scanner in the two directions of a horizontal direction and a vertical direction, in this case, there is a problem in that the constitution and control of the scanning system becomes complicated.
Therefore, there has been proposed a scanning-type image display device provided with two sets of scanners each scanning light in one dimension so as to incorporate horizontal scanning and vertical scanning, respectively.
Conventionally, it is normal to use a polygon mirror or a galvano-mirror for a scanner of the both directions. A projection device that employs a polygon mirror in scanner of the both directions is disclosed in Japanese Unexamined Patent Application No. H01-245780.
Although a device that uses a polygon mirror is introduced in Japanese Unexamined Patent Application No. H01-245780, increasing the resolution of an image format entails higher scanning frequencies, which approaches the limits of a polygon mirror or a galvano-mirror.
Therefore, in recent years systems have been announced that utilize Micro Electro Mechanical Systems (MEMS) technology in high-speed scanners.
A scanner that utilizes MEMS technology (hereinafter simply referred to as a “MEMS scanner”) is one manufactured utilizing micro-processing technology of a semiconductor material, such as silicon, and drives a mirror supported by a torsion spring or the like with electrostatic force or the like.
This scanner can scan light by causing the mirror to travel in a reciprocating motion via the interaction of the electrostatic force and the restoring force of the spring.
By using a MEMS scanner, it is possible to achieve a scanner that can be operated at a high frequency and large deflection angle compared to a conventional scanner. Thereby, it is possible to display high-resolution images.
In order to realize scanning with a high speed MEMS scanner, since the mirror must be made to travel in a reciprocation manner at the resonance point, assuming a given resolution, it is necessary to design and fabricate the resonance point of the mirror so as to agree with that resolution.
On the other hand, in viewpoint from the video software, many video formats have in recent years come into wide use with different resolutions, scan modes (interlaced, progressive, etc.) and screen aspect ratios or the like. Consequently, there is a demand from users to watch different video formats on a single image display device.
However, as stated above, since MEMS scanners are manufactured to meet a specific resolution, when a video format having other than the intended resolution is input to the image display device, there are problems in that the image is reduced on the screen, and the entire image is not displayable, or the image distortion occurs because the horizontal scanning and vertical scanning cannot be synchronized.
While there are methods of performing resolution conversion by image processing so as to prevent such problems, in this case an enormous load on the image processing circuit.
Examples of problems in the case of using a MEMS minor were given above, but these problems are not limited to a device using a MEMS mirror, being common to devices that use other resonant-type scanners such as a resonant-type galvanomirror or the like.